It is widely known to make built-in-place reinforced concrete piles by a method wherein a borehole is formed in the ground by using any appropriate equipment and then a reinforcement is placed in the borehole. Subsequently, the borehole is filled with a concrete mix which is then positively compacted by means of vibrators to obtain a pile.
In making the borehole in the ground, the borehole diameter is always determined by the desired diameter of the pile. As the drilling of vertical and inclined boreholes is always associated with the employment of cumbersome equipment, the construction of large diameter piles (more than 300 mm) requires much labor and completely excludes any opportunity of working in rather inaccessible places (e.g. when making pile foundations in expanding factory buildings or on other sites occupied by buildings, as well as in consolidating railway beds).
In addition, during the placing of concrete in the borehole and compacting the concrete mix, the reinforcement tends to be displaced from the desired position so that the load-carrying capacity of the pile is considerably reduced.
Ensuring the desired strength of structures to be built requires the number of piles used to be increased, or the piles to be made more bulky.